Thyroid hormone negatively regulates the transcriptional activity of the beta-amyloid precursor protein gene

The expression of the beta-amyloid precursor protein (APP), which plays a key role in the development of Alzheimer's disease, is regulated by a variety of cellular mediators in a cell-dependent manner. In the present study, we present evidence that thyroid hormones negatively regulate the expression of the APP gene in neuroblastoma cells. Transient transfection studies using plasmids that contain progressive deletions of the 5' region of the gene demonstrate that triiodothyronine (T3), the more active form of the thyroid hormones, represses APP promoter activity by a mechanism that requires binding of the nuclear T3 receptor (TR) to a specific sequence located in the first exon. The unliganded receptor increases promoter activity, and T3 reverses that activity to basal levels. The repressive effect of T3 does not exhibit TR isoform specificity, and it is equally mediated by TRalpha and TRbeta. Gel mobility shift assays using in vitro synthesized nuclear receptors and nuclear extracts led to the identification of a negative thyroid hormone response element, at nucleotide position +80/+96, that preferentially binds heterodimers of TR with the retinoid X receptor. Insertion of sequences containing this element confers negative regulation by T3 to a heterologous TK promoter, thus indicating the functionality of the element.     

Epstein-Barr virus protein LMP2A regulates reactivation from latency by negatively regulating tyrosine kinases involved in sIg-mediated signal transduction

Like other herpesviruses, Epstein-Barr Virus (EBV) persists in its host through an ability to establish latent infection with episodic reactivations. In latent infection EBV expresses an integral membrane protein LMP2A that regulates reactivation from latency. LMP2A is constitutively tyrosine phosphorylated and is associated with lyn and syk tyrosine kinases. The activity of lyn is substantially reduced. In EBV-infected cells in which LMP2A is expressed, crosslinking of sIg fails to trigger the protein tyrosine kinase signal cascade, tyrosine phosphorylation of cell proteins does not change, second messengers are not generated, and lytic EBV infection is not induced. In contrast, crosslinking of sIg on cells infected with EBV recombinants with null mutations in LMP2A results in transient tyrosine phosphorylation of lyn, syk, phospholipase C gamma 2 and phosphatidylinositol-3' kinase, transiently increased intracellular free calcium, and reactivation of lytic EBV infection. These studies describe a novel molecular regulator of herpesvirus latency and focus attention on the importance of transmembrane signal transduction in herpes virus reactivation from latency. They support the working hypothesis that the identification of ligand-receptor interactions that can result in the induction of reactivation will provide an important inroad toward the delineation of the molecular mechanism, which govern herpesvirus reactivation from latency.     

Both Epstein-Barr viral nuclear antigen 2 (EBNA2) and activated Notch1 transactivate genes by interacting with the cellular protein RBP-J kappa

The Epstein-Barr viral nuclear antigen 2 (EBNA2) plays a key role during establishment and maintenance of B cell immortalization after Epstein-Barr virus (EBV) infection. EBNA2 acts as a transactivator of cellular and viral genes. We studied two EBNA2 regulated viral promoters (TP1 promoter and LMP/TP2 promoter) in detail to learn more about the molecular mechanisms of EBNA2-mediated transactivation. In both promoters we could identify at least one binding site for the cellular repressor protein RBP-J kappa. EBNA2 is tethered to the EBNA2 responsive promoter elements by interaction with this cellular protein. Although necessary, the binding of RBP-J kappa is not sufficient for EBNA2-mediated transactivation. At least two further cellular proteins, which are different in the studied promoters are important for efficient transactivation. The identification of RBP-J kappa as central mediator of EBNA2 transactivation suggested an interference of EBNA2 with the highly conserved Notch receptor signal transduction pathway. We could show that an activated form of the Notch receptor can transactivate a reporter construct containing a hexamer of the two RBP-J kappa binding sites of the TP1 promoter supporting the idea that EBNA2 acts as a functional equivalent of an activated Notch receptor.     

Phosphorylation of the vesicle docking protein p115 regulates its association with the Golgi membrane

The vesicle docking protein p115 was found to be phosphorylated in a cell cycle-specific manner; it was found phosphorylated in interphase but not in mitotic cells. During interphase, however, two forms of p115 were detected in the cells; the phosphorylated form was found exclusively in cytosol, whereas the unphosphorylated form was associated with membranes, mostly of the Golgi complex. The latter form was released from the membranes upon phosphorylation. Mutational analysis revealed that the phosphorylation site of p115 was the Ser942 residue in the C-terminal acidic domain. A mutant with a single substitution of Ser942 --> Ala markedly increased its association with the Golgi membrane. Another mutant with Ser942 --> Asp was able to associate with the membrane, although at a decreased level, indicating that the dissociation of p115 from the membrane is not simply due to the negative charge of phosphorylated Ser942. Taken together, these results suggest that the phosphorylation of Ser942 at the C-terminal acidic domain regulates the interaction of p115 with the Golgi membrane, possibly taking part in the regulatory mechanism of vesicular transport.     

Activation of amylin gene transcription by LIM domain homeobox gene isl-1

The main objective of the Ambulatory Blood Pressure and Treatment of Hypertension (APTH) trial is to test the hypothesis that antihypertensive treatment based on ambulatory monitoring may be more beneficial than treatment guided by conventional sphygmomanometry. After a 2-month run-in period on single-blind placebo, hypertensive patients were randomized to two groups, one in which the target pressure was a sitting diastolic pressure from 80 through 89 mm Hg on conventional sphygmomanometry (conventional blood pressure [CBP] group), and one in which a daytime (from 10 to 20 h) diastolic pressure from 80 through 89 mm Hg had to be achieved (ambulatory blood pressure [ABP] group). After randomization all patients were started on lisinopril 10 mg/day. One month later lisinopril could be continued at 10 or 20 mg/day or discontinued depending on the attained blood pressure level. This article is an interim report on 207 patients followed for two months into the trial. At one month lisinopril was discontinued more frequently in the ABP than the CBP group (24 vs 9 patients, p = 0.004). Nevertheless at two months, blood pressure control was not significantly different in the two treatment groups. The baseline-adjusted differences in systolic pressure between the two treatment arms of the trial (ABP-CBP group) were +2.7 mm Hg (95% confidence interval [CI]): -2.9, +8.3) for the conventional pressure, +0.4 mm Hg (CI: -4.3, +5.1) for the 24 h pressure, -0.1 mm Hg (CI: -5.1, +4.8) for the daytime pressure and -0.7 mm Hg (CI: -6.7, +5.4) for the night-time pressure. The corresponding differences in diastolic pressure were -1.3 mm Hg (CI: -4, +1.4), +0.1 mm Hg (CI: -3, +3.1), -1.1 mmgH (CI: -4.4, +2.1) and +0.3 mm Hg (CI: -3.7, +4.3), respectively. Thus, the present findings do not refute the APTH research hypothesis. In terms of blood pressure control and the number of patients remaining on antihypertensive drugs, treatment based on ambulatory recordings may be preferable to treatment guided by conventional sphygmomanometry.     

Itk negatively regulates induction of T cell proliferation by CD28 costimulation

Effects of epidermal growth factor (EGF) and possible mechanisms of EGF-mediated signal transduction were investigated in isolated cells of the digestive gland of the mussel (Mytilus galloprovincialis Lam. ). EGF induced a cytosolic Ca2+ transient and subsequently stimulated DNA synthesis; both effects were dose-dependent in the nanomolar range and inhibited by pretreatment with an inhibitor of tyrosine kinase activity, suggesting specific EGFR-like receptors. The EGF-induced cytosolic Ca2+ transient was mainly due to a Ca2+ influx through the plasma membrane, possibly involving voltage-insensitive Ca2+ channels. Such a Ca2+ response was abolished by pretreatment with indomethacin and NDGA, inhibitors of arachidonic acid metabolism; similarly, the EGF-stimulated increase in DNA synthesis was significantly reduced. Indomethacin, a cyclooxygenase inhibitor, had the greatest effect on both EGF-induced responses. Results suggest the presence of EGF-responsive cells in the mussel digestive gland. A possible role for arachidonic acid and its metabolites in mediating the effects of EGF is also indicated.